The present invention relates to electronically controlled throttles for vehicle engines. In particular, the present invention relates to systems for detecting throttle failures.
A throttle controls the flow of air, or air and fuel, inducted into an internal combustion engine, and thereby controls the power produced by the engine. Engine power defines the speed of the engine or vehicle to which it is attached, under a given load condition, and thus, reliable control of the throttle setting is important.
In prior art mechanical systems, a direct mechanical linkage controlled the throttle, typically in the form of a cable running from the accelerator pedal, operable by the user of the vehicle, to the throttle. Absent tension on the cable from the pedal, the throttle would revert to an idle opening (i.e., a default position) under the influence of a biasing spring. The idle opening provides sufficient inducted air and gas to permit low speed operation of the engine under no- or low-load conditions.
Although mechanical linkages are simple and intuitive, they are not readily adapted to electronic control of an engine such as may be desired in sophisticated emissions reduction systems or for features such as automatic vehicle speed control. For these purposes, the mechanical linkage may be replaced with electrical wiring carrying operator input signals from a position sensor associated with the accelerator pedal to a throttle controller, which in response sends throttle command signals to an electric motor (or other actuator) actuating the throttle. The operator input signals and throttle command signals may be monitored for loss or faults to provide greater reliability to the system.
While electronic control without mechanical linkages allows for a variety of desirable features, the removal of mechanical linkages eliminates the mechanical feedback such linkages provide. Throttle position is no longer physically tied to the operator""s movement of the accelerator pedal. Because throttle operation is critical to vehicle operation, alternate mechanisms must be developed to determine whether a vehicle""s throttle is operating in accordance with the throttle command signals derived from the operator input signals (and also in accordance with other commands provided by computer or other control elements within the vehicle).
Unfortunately, the design of such mechanisms is not simple. In the absence of dynamics, it would be possible to test whether a throttle was operating in accordance with throttle command signals simply by comparing the actual (i.e., measured) throttle position with the commanded throttle position. However, in practice, actual throttle position seldom equals commanded throttle position since there is usually (at least) some minimal error associated with the operation of the electric motor (in actuating the throttle), with the throttle position sensor or with some other element. In particular, the electric motor cannot respond instantaneously to changes in the throttle command signals. Actual throttle position often lags or overshoots changes in commanded throttle position. Therefore, a simple throttle monitoring mechanism that compares actual throttle position directly with commanded throttle position will too frequently find the throttle to be operating improperly.
Moreover, the acceptable, expected differences between actual throttle position and commanded throttle position are not within a constant error band, but rather dynamically change with the operation of the throttle. In particular, as the magnitude and frequency of changes in the throttle command signals increase, the difference between actual throttle position and commanded throttle position becomes even more pronounced. Therefore, a simple throttle monitoring mechanism that compares actual throttle position with the commanded throttle position plus (or minus) a constant error band also will too frequently find the throttle to be improperly operating even though the deviation between the actual throttle position and commanded throttle position is within an acceptable, expected range (unless the error band is made so large as to render the throttle monitoring mechanism overly tolerant).
Given the importance of determining whether a throttle is operating in accordance with throttle command signals, it would be advantageous to develop a throttle monitoring mechanism that accurately determined when the throttle was operating improperly. It would further be advantageous if such a mechanism was capable of determining improper throttle operation and yet at the same time was capable of ignoring expected deviations between actual throttle position and commanded throttle position due to acceptable levels of throttle lag, throttle overshoot and other error.
The present inventor has recognized that, for a throttle monitoring mechanism to both accurately determine improper throttle operation and be tolerant of expected deviations from ideal throttle performance, it would be desirable if the throttle monitoring mechanism was configured to allow for greater deviations between the actual and commanded throttle positions when such greater deviations were expected (i.e., when there were large and/or frequent changes in the throttle command signals), and to allow for only smaller deviations between the actual and commanded throttle positions when only such smaller deviations were expected.
The present invention therefore relates to a throttle error detection system for determining when a position of a throttle is not adequately conforming to a command signal provided by a control module such that a fault indication should be provided. The system includes a throttle assembly including the throttle, which is configured to generate a position signal indicative of the position of the throttle. The system further includes a processor that is coupled to the throttle assembly and is configured to receive the command signal and the position signal. The processor is further configured to determine a first limit that is functionally dependent upon the command signal, where the first limit delimits an acceptable range of throttle positions from a first unacceptable range of throttle positions. The processor determines that the position of the throttle is not adequately conforming to the command signal when the position of the throttle as indicated by the position signal is in the first unacceptable range of throttle positions.
The present invention further relates to, in a vehicle, a method of determining when a position of a throttle is not adequately conforming to a command signal provided by a control module. The method includes receiving the command signal at a processor, and receiving a position signal indicative of the position of the throttle at the processor. The method additionally includes determining at the processor a first limit that is functionally dependent upon the command signal, where the first limit delimits an acceptable range of throttle positions from a first unacceptable range of throttle positions. The method further includes determining that the position of the throttle is not adequately conforming to the command signal when the position of the throttle as indicated by the position signal is in the first unacceptable range of throttle positions.
The present invention additionally relates to, in a vehicle, a system for determining when a position of a throttle is not adequately conforming to a command signal provided by a control module. The system includes a means for calculating a limit that is functionally dependent upon the command signal, where the limit demarcates an acceptable range of throttle positions from an unacceptable range of throttle positions. The system further includes a means for comparing a position signal indicative of the position of the throttle to the first limit, and a means for determining that the position of the throttle is not adequately conforming to the command signal when the position signal goes beyond the limit. The means for calculating the limit adjusts the limit in a direction tending to expand the acceptable range of throttle positions immediately when the command signal, adjusted by an error band, changes to enter the unacceptable range of throttle positions, and adjusts the limit in a direction tending to reduce the acceptable range of throttle positions when the command signal changes to move away from the unacceptable range of throttle positions.